The invention relates to a cardan drive for connecting a power take-off (PTO) of an agricultural vehicle to an input shaft of an agricultural implement.
A cardan drive is a drive wherein one or more shafts connect a first and a second rotating element, wherein at least one universal joint is used in the connection. Agricultural vehicles such as tractors are typically provided with a power take-off (PTO). The PTO is formed by a shaft located on an outer side of the tractor and which can be driven by the tractor engine. This shaft is typically provided with toothing such that a rotating movement can be transmitted to an external element. This external element, typically an implement which is attached behind the tractor or suspended on the tractor, can then be driven and/or provided with energy via the PTO. Agricultural implements typically have an input shaft via which the implement can be driven or provided with energy. This input shaft is connected via a transmission to the PTO when the implement is connected to the tractor. This connection is typically made via a cardan drive.
Different cardan drives are known from the prior art. Two shafts can typically be provided in the cardan drive, a primary shaft and a secondary shaft. The primary shaft is connected with one end to the PTO of the tractor, and with another end to the secondary shaft. The secondary shaft is then connected with its other end (the first end being connected to the primary shaft) to the input shaft of the implement. The primary shaft typically lies here at an angle to the secondary shaft. Different couplings are known for transmitting a rotating movement of the primary shaft through an angle to the secondary shaft. An example thereof is a universal joint. In a universal joint two yokes are placed over each other at a right angle, and a cross-shaped element is connected via roller bearings to the prongs of the yokes. When a universal joint is used however, the rotation speed is not transmitted proportionally from the primary shaft to the secondary shaft, and the secondary shaft will have a sinusoidal rotation speed. A double universal joint is therefore used. Known is a double universal joint for the purpose of enabling a homokinetic connection between a primary and a secondary shaft. A homokinetic connection is here a connection wherein the input speed and the output speed are directly proportional.
Double universal joints are known on the market and are also referred to as CV joints. In such CV joints an intermediate element of the double universal joint (the intermediate element is formed by the middle two yokes) is automatically held in a correct position. This is because the rotation angle of the intermediate element has to lie in the middle between the primary and secondary shafts. When the angle between the primary shaft and the secondary shaft becomes greater and the power which is transmitted increases (as is the case with agricultural implements), known CV joints break due to overload. The force on the angle positioning means of the intermediate element in the CV joint in particular becomes greater than the maximum force which the CV joint is able to bear. As a result it is not always possible to use CV joints.